Scintillation detectors or direct-conversion semiconductor detectors are used for the detection of gamma and X-ray radiation, in particular in CT and dual energy CT systems. In the scintillation detectors, the incident radiation is detected indirectly by means of the excitation of electrons and the conversion into photons. By contrast, the direct-conversion detectors based on semiconductor materials such as CdTe, CdZnTe, CdTeSe and CdZnTeSe, for example, are able to count individual photons, and hence detect the radiation directly. In this case, the semiconducting detector material is electrically conductively connected to the read-out electronics and the voltage supply of the detector by way of platinum or gold contacts. However, since these contacts do not constitute ideal ohmic contacts, that is to say have different excitation energies of the charge carriers, injection of holes occurs in the case of platinum contacts and injection of electrons occurs in the case of gold contacts. This means that charge carriers are accumulated in the semiconductor. The formation of a space charge occurs, which impedes the separation and the transporting-away of the charge carriers produced by irradiation.
The space charge therefore leads to an amplification of the effect of polarization. Polarization is understood to mean the reduction of the electric field by stationary charges that are generally bound to deep defects. These deep defects can trap the charge carriers generated by radiation and recombine with them. A significantly lower intensity of the radiation is thus suggested. The polarization accordingly limits the maximum detectable flux of a direct-conversion detector.
Consequently, the performance of the detector is greatly restricted. High radiation densities such as occur in computed tomography, for example, cannot be converted into electrical pulses directly and losslessly, such that the use of direct-conversion semiconductor detectors in CT systems still does not yield completely exact measurement results.
At the present time, in the prior art there is no known possibility for realizing an ideal ohmic contact between the semiconducting detector material and some other contact material.